Mobile communication devices are typically identified by unique identifiers known as IMEIs (International Mobile Equipment Identifiers). An IMEI is a 15-digit number that uniquely identifies a corresponding device when the device is used on a GSM (Global System for Mobile Communications) cellular communication network. Device manufacturers cooperate to ensure that no two devices have the same IMEI.
Each cellular communication operator maintains a database listing the IMEIs of devices that have been authorized for use on the communication network of the carrier. This database, known as an EIR (Equipment Identity Register), also indicates the IMEIs of any devices that should not be allowed to access the communication network. For example, IMEIs corresponding to devices that have been reported lost or stolen are marked as being blocked, and the devices are prevented from operating on the communication network. This discourages device theft, because stolen devices are unable to register for and obtain the services of the communication network.